1. Field of the Invention
The present invention relates to a television signal multiplexing and demultiplexing system for multiplexing and demultiplexing additional information utilized for implementing additional features, such as a high-definition picture and a wide picture frame, in a television broadcasting system.
2. Description of the Related Art
In the field of television broadcasting, intensive research and development for the production of high-quality television pictures have been made recently.
Ways of producing a high-quality television picture include making the aspect ratio of the TV picture frame larger and making the definition of a TV picture higher. By making the aspect ratio of TV picture frame larger than the existing aspect ratio, it becomes possible to achieve a high-quality TV picture in terms of the sense of presence as obtained from a wide picture. In the case of the high-definition TV picture, on the other hand, the bandwidth of a TV signal is made greater, whereby a high-quality TV picture is achieved in terms of horizontal resolution of the picture.
Even if the greater-aspect-ratio broadcasting system and/or the high-definition broadcasting system is realized, it is desirable that compatibility with the existing broadcasting systems be taken into account. This is because the newly developed broadcasting system and the existing broadcasting system are considered to exist simultaneously for the time being.
In order to keep the new broadcasting system and the existing broadcasting system compatible, additional information adapted for implementing the greater aspect ratio and/or higher definition may be multiplexed with a television signal of the existing broadcasting system. Moreover, it is desired that the multiplexing be performed within the baseband of the television signal of the existing broadcasting system. This is to allow existing television broadcasting equipment to deal with a television signal of the new broadcasting system as it is.
An exemplary system for multiplexing, as additional information, information adapted to implement the greater aspect ratio with a television signal of the existing broadcasting system within its baseband is disclosed in Japanese Patent Application No. 63-56850 (hereinafter referred to as reference 1).
In the multiplexing system disclosed in reference 1, diagonal high-frequency components of a luminance signal of the NTSC system are used, both in a still picture and a motion picture, to multiplex the additional information for the greater aspect ratio.
A system for multiplexing, as additional information, information for implementing the high-definition with a television signal of the existing broadcasting system is disclosed, for example, in "Fully Compatible EDTV for Improving Both Y and Color signals by Using a Single New Subcarrier", IEEE Transaction on Consumer Electronics, Vol. 34, No. 3, AUGUST 1988 (hereinafter referred to as reference 2).
In the multiplexing system disclosed in reference 2, information for high definition is multiplexed with a television signal of the NTSC system at the time of production of a still picture.
The information for high definition includes a high-definition component (hereinafter referred to as a YH component) contained in a luminance signal and a high-definition component (hereinafter referred to as a QH component) contained in a Q signal which is one of color difference signals.
FIG. 7 illustrates a vertical-time spectrum representing multiplexing regions for the YH and QH components. The YH component is multiplexed in spectral regions of the first and third quadrants which are unused at the time of a still picture. On the other hand, the QH component is multiplexed with diagonal high-frequency components having a vertical frequency of 525/2 [cph]. Note that QH' is a reflected component due to interlaced scanning of the QH component. The reflected component QH' appears in positions corresponding to a time frequency of 30 [Hz].
According to the multiplexing system, the horizontal resolution of a still picture can be increased. However, the horizontal resolution of a motion picture cannot be increased because additional information cannot be multiplexed at the time of production of a motion picture. This is because, in the case of a motion picture, the spectrum spreads in the direction of the time axis so that a television signal and additional information are superimposed upon each other and thus cannot be separated from each other on the receiving side. However, even if additional information can be multiplexed only at the time of production of a still picture, it will not be a serious problem because the high-definition version of a picture is effective in a still picture but not so effective in a motion picture.
The foregoing relates to conventional exemplary multiplexing systems for making the aspect ratio of a picture frame greater and for making the definition of a picture higher.
In making the picture quality high it is desired that both of the greater-aspect-ratio picture system and the high-definition picture system be adopted. To this end, it will occur to us to adopt both of the above-described multiplexing systems simultaneously.
Since, however, the multiplexing region for the additional information for the great aspect ratio in reference 1 and the multiplexing region for the QH component in reference 2 are identical with each other, the two multiplexing systems cannot be adopted simultaneously. To solve this problem, it is required to make the multiplexing region for the additional information in reference 1 and the multiplexing region for the QH component in reference 2 differ from each other.
However, each of the multiplexing system in reference 1 and the multiplexing system reference 2 is a system in which a specific region for diagonal high-frequency components is merely removed and then additional information is multiplexed in the region. Thus, the multiplexing systems are adaptable to the case where one piece of additional information is multiplexed or the case where plural pieces of additional information differing in horizontal band are multiplexed but not adaptable to the case where plural pieces of additional information of the same horizontal band are multiplexed. This is because, in such a case, the plural pieces of additional information are superimposed upon one another and cannot be separated from one another at the receiving end.